The conventional catalyst assembly for cleaning the exhaust gas of an automotive vehicle includes a catalyst or catalyst carrier (hereinafter referred to simply as the catalyst) having a honeycomb shape or a monolithic structure. This catalyst is secured inside the catalyst muffler by means of a mat or mats of ceramic fiber material or a resilient metal screen, both of which are mounted in the space between the catalyst and the catalyst muffler to serve as a cushioning material. Various arrangements are made to safeguard the catalyst muffler against destruction resulting from vibration and compensate for thermal expansion of the catalyst muffler.
However, the above process of providing mats of ceramic fiber around the catalyst has a defect in that the filling material is liable to contract as a consequence of vibration to form a gap between the filling material and the catalyst. The filling material then ceases to function effectively as a cushioning material. Moreover, when mats of ceramic fiber are used as filling material, a small quantity of exhaust gas flow unavoidably through the layers of filling material, thus causing particles of ceramic fiber to become entrained in the stream of exhaust gases and decreasing the effectiveness of the catalyst converter due to the flow of gas through the gap so formed.
On the other hand, when a resilient metal screen is coiled about the catalyst, the latter is subjected to a higher concentrated load under vibration at the points of contact with the metal screen, thus causing local cracks in the catalyst and shortening its service life. In addition, the catalyst used in the exhaust gas cleaner of the automotive vehicle is heated to a high temperature of 600.degree. to 700.degree. C. during usage, and the metal screen is also heated close to this temperature. This method is therefore disadvantageous economically as the metal screen must be fabricated from a material of higher quality to be used effectively as a cushioning material when subjected to these elevated temperatures.